Human lung squamous cell carcinoma (SCC) is highly associated with increased pulmonary macrophage infiltration. Previously, we showed that marked pulmonary infiltrating macrophages were required for spontaneous lung SCC development in a mouse model (L-IkkaKA/KA, KA/KA) that resembles human lung SCC. Interestingly the lung SCC-associated macrophages specifically express elevated inducible nitric-oxide-synthase (NOS2). However, the role of macrophage NOS2 in lung carcinogenesis has not been explored. Here, we show that NOS2 ablation inhibits macrophage infiltration, fibrosis, and SCC development in the lungs of KA/KA mice. Macrophage NOS2 was found to circulate inflammation and enhance macrophage migration and survival. NOS2 promotes foam macrophage formation characterized with impaired lipid metabolism. NOS2 null bone marrow transplantation reduces foam macrophage numbers and carcinogenesis in KA/KA chimaeras. This finding sheds light on a new mechanism by which macrophage NOS2 increases pulmonary inflammatory responses and macrophage survival and impairs macrophage lipid metabolism, thereby promoting lung SCC formation. Lung adenocarcinoma (ADC) and squamous cell carcinoma (SCC) are two distinct and predominant types of human lung cancer. IKKa has been shown to suppress lung SCC development, but its role in ADC is unknown. We found inactivating mutations and homologous or hemizygous deletions in the CHUK locus, which encodes IKKa, in human lung ADCs. In mice, lung-specific Ikka ablation (Ikka-Lu) induces spontaneous ADCs and promotes KrasG12D-initiated ADC development, accompanied by increased cell proliferation, decreased cell senescence, and reactive oxygen species (ROS) accumulation. IKKa deletion upregulates NOX2 and downregulates NRF2, leading to ROS accumulation and blockade of cell senescence induction, which together accelerate ADC development. Pharmacological inhibition of NADPH oxidase (NOX) or ROS impairs KrasG12D-mediated ADC development in Ikka-Lu mice. Therefore, IKKa modulates lung ADC development by controlling redox regulatory pathways. This study defines that IKKa functions as a novel suppressor of lung ADC in human and mice through a unique mechanism that regulates tumor cell-associated ROS metabolism.